1
Introduction

Although significant steps have been taken over the last 15 years to reduce the size and frequency of oil spills, the sheer volume of petroleum consumed in this country and the complex production and distribution network required to meet the demand make spills of oil and other petroleum products inevitable (NRC, 2003). Oil spill contingency plans, therefore, specify appropriate response to spills whenever and wherever they occur. Spill response in the United States has traditionally focused primarily on physical containment and recovery approaches. For spills on water, these approaches emphasize controlling and recovering spilled oil or petroleum products through the deployment of mechanical equipment such as booms and skimmers.

The effectiveness of mechanical response techniques is variable and highly influenced by the size, nature, and location of the spill as well the environmental conditions under which the response is carried out. Essentially, mechanical response works satisfactorily under a finite subset of all possible spill scenarios. The spill response community has worked to expand the subset of spill scenarios where effective response can be mounted, through improving the quality, and to some degree, the quantity of mechanical equipment available to respond to a spill, and training and coordination of efforts. In addition, other non-mechanical techniques have been developed and tested. The two most commonly considered non-mechanical techniques include in-situ burning and the use of chemical dispersants.

In-situ burning refers to the controlled burning of oil close to where the spill occurred. For spills on open water, the oil must be collected and

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1
Introduction
Although significant steps have been taken over the last 15 years to reduce the size and frequency of oil spills, the sheer volume of petroleum consumed in this country and the complex production and distribution network required to meet the demand make spills of oil and other petroleum products inevitable (NRC, 2003). Oil spill contingency plans, therefore, specify appropriate response to spills whenever and wherever they occur. Spill response in the United States has traditionally focused primarily on physical containment and recovery approaches. For spills on water, these approaches emphasize controlling and recovering spilled oil or petroleum products through the deployment of mechanical equipment such as booms and skimmers.
The effectiveness of mechanical response techniques is variable and highly influenced by the size, nature, and location of the spill as well the environmental conditions under which the response is carried out. Essentially, mechanical response works satisfactorily under a finite subset of all possible spill scenarios. The spill response community has worked to expand the subset of spill scenarios where effective response can be mounted, through improving the quality, and to some degree, the quantity of mechanical equipment available to respond to a spill, and training and coordination of efforts. In addition, other non-mechanical techniques have been developed and tested. The two most commonly considered non-mechanical techniques include in-situ burning and the use of chemical dispersants.
In-situ burning refers to the controlled burning of oil close to where the spill occurred. For spills on open water, the oil must be collected and

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held by fire-resistant booms or trapped in ice to ensure that the oil has a minimum thickness to be ignited and sustain burning. The advantages of in-situ burning include rapid removal of oil and no need for oil recovery, transport, storage, and disposal. The major disadvantages of in-situ burning include the black smoke, difficulties of collecting and containing a large amount of the oil to burn, lower effectiveness as the oil weathers (spreads, emulsifies), and sensitivity to sea state and weather conditions that reduce the viability of all response options (Michel et al., 2004). Worldwide, there have been 43 known intentional in-situ burns of oil on water (Fingas, 1999b; Michel et al., 2004). Of these, only thirteen were actual spills (the rest were planned tests). Of these, four were in ice, two were attempts to burn the oil inside the holds of the ship (Torrey Canyon and New Carissa), and four were of uncontained slicks. In the United States, the only on-water in-situ burning at a spill was the 1989 test burn during the Exxon Valdez oil spill, which was the first time a fire-resistant boom was used at a spill (Michel et al., 2004).
Dispersants are chemical agents (surfactants, solvents, and other compounds) that reduce interfacial tension between oil and water in order to enhance the natural process of dispersion by generating larger numbers of small droplets of oil that are entrained into the water column by wave energy. The small dispersed oil droplets tend not to merge into larger droplets that quickly float back to the water surface and reform into surface slicks. Instead, the small droplets stay suspended in the water column, spreading in three dimensions instead of two and being distributed by turbulent diffusion.
The use of chemical dispersants, as well as in-situ burning, revolves around changing the fate of spilled material within the environment, as opposed to attempting recovery or removal of that material from the environment. They are therefore generally viewed in the United States as secondary options intended to support or supplement mechanical response, and requiring risk-based decisionmaking at the time of a spill.
Early efforts to disperse oil slicks on water and along shorelines used degreasing agents or detergents that contained highly toxic components and resulted in high mortality to rocky shore communities (Smith, 1968). Recent formulations are much less toxic such that the toxicity associated with dispersed oil droplets is essentially a function of the toxicity of the oil itself. As a consequence, U.S. policymakers have been exploring the potential for dispersant use for nearly two decades. In 1989, the National Research Council released Using Oil Spill Dispersants on the Sea. That report focused on the possible effects and effectiveness of using dispersants to combat spills in open waters. Highlighting a number of specific research efforts that should be pursued, one of the report recommendations was that “dispersants be considered as a potential first response option”

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to large spills in the open ocean. Because dispersant effectiveness diminishes as the spilled oil weathers, it was recommended that regulations and contingency planning make rapid response possible. It was recognized that the availability of both dispersant and the equipment needed to apply it greatly influenced the potential to use dispersants during the critical window of opportunity following a spill. Many countries, including France, South Africa, Canada, New Zealand, Norway, and the United Kingdom, have established standards regarding the use of chemical dispersants and adopted specific decision-making processes to evaluate the appropriateness and effectiveness of use under given situations and with specified types of oils. Approaches vary among countries, reflecting biophysical differences as well as differing cultural values regarding the appropriateness of using chemical dispersants to combat oil spills.
FOCUS OF CURRENT STUDY
Although the chemical processes by which dispersants work are generally well understood, their effectiveness is limited to varying degrees by the type of oil spilled and the environmental conditions at the time and location of a spill, as well as the timing and method of application. In general, the information base used by decisionmakers dealing with spills in areas where the consequences of dispersant use are fairly straightforward, has been adequate (for example, situations where rapid dilution has the potential to reduce the possible risk to sensitive habitat enough to allow the establishment of pre-approval zones). Many of the technical issues raised in this report, however, deal with settings where greater confidence is needed to make effective decisions regarding potential benefits or adverse impacts associated with dispersant use. In many instances where a dispersed plume may come into contact with sensitive water-column or benthic organisms or populations, the current understanding of key processes and mechanisms is inadequate to confidently support a decision to apply dispersants.
While laboratory experiments over the last decade or so have shed some light on how, when, and where dispersants can be effective, the use of non-standardized laboratory or mesocosm testing and monitoring techniques, lack of sufficiently coordinated effort, and misinterpretation of available information, have limited development of consensus about dispersant efficacy in some settings (e.g., freshwater, estuarine, coastal, and high-latitude environments). The lack of standardized procedures, when coupled with an insufficient number of well-designed tank or field-scale tests, has limited the value of this research for decisionmaking. In addition, there has been insufficient research into the fate of both chemically and naturally dispersed oil to evaluate concerns about its long-term im-

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pact. There are many unanswered questions about what happens to the oil droplets after they mix into the water column, such as the extent to which they will they bind to sediment or be ingested by organisms, how quickly they degrade, and what are the final degradation products.
Typically, the effects of oil spills have been very apparent on shorelines and coastal megafauna (e.g., birds and otters). The potential effects of dispersed oil on benthic flora and fauna (e.g., seagrasses, corals, and clams), fish populations, and the trophic relationships among these species, are less documented. Thus, while the use of dispersants is assumed to reduce the threat posed to some portions of the ecosystem (e.g., marine mammals and birds that frequent the air-water interface where oil slicks form), it is not clear in many instances how changing the fate of oil alters the potential threat to other portions of the ecosystem (e.g., fish and other fauna in the water column and on the seafloor) that are exposed to the dispersed oil plume. In deep open-water settings (deeper than 10 m or roughly 30 feet)1 where there is rapid dilution of the dispersed oil, impacts to water-column and benthic resources are likely to be low, thus most of the pre-approval zones are defined in terms of distance offshore and minimum water depths.
While nearly every marine Area Contingency Plan (development of the plans was mandated by the Oil Pollution Act of 1990 [OPA 90]) includes flowchart-like decision trees and pre-approval for use of dispersants in offshore waters (e.g., >3 nautical miles [just over 5 km] and deeper than 10 m [about 30 ft]), there appears to be minimal risk assessment and decision-making procedures in place for spills in coastal and estuarine waters. Improving response to nearshore spills is particularly important as the majority of spills of all sizes in the United States occur within 3 nm of the shoreline (see Figure 1-1; NRC, 2003). Kucklick and Aurand (1997) conducted an assessment of the spills from 1973 to 1994 to determine the number of historic spills where dispersant use might have been appropriate, using the following criteria: >1,000 barrels (roughly 130 tonnes) of a dispersible oil, weather conditions, and distance from shore. Of the 69 crude oil spills meeting their criteria, only 10 percent were greater than 3 miles offshore, thus dispersant use in nearshore waters will be a common consideration. While dispersant use generally presents greater risks in shallower, nearshore settings, the likelihood that untreated nearshore
1
Conversions reported in the text conserve the number of significant figures of the original reported value using rules consistent with the NRC report Oil in the Sea III: Inputs, Fates and Effects (NRC, 2003) and available on the following Massachusetts Institute of Technology website: http://web.mit.edu/10.001/Web/Course_Notes/Statistics_Notes/Significant_Figures.html. See Appendix D for additional information on definitions and unit conversions used through out this report.

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FIGURE 1-1 Frequency distribution of oil spills of various size classes (in gallons) in U.S. marine waters for 1990–1999. Note that for all size classes, spills more frequently occur in nearshore locations (less than 3 miles from shore) than offshore (3–200 miles from shore). These are the same data used to develop trends reported in Oil in the Sea III (NRC, 2003).
SOURCE: Data and figure provided by D. Etkin, Environmental Research Consulting.
spills may impact coastal resources is also much greater. Thus, the increased complexity of dispersant use decisions in nearshore settings is accompanied by a greater need to make the most appropriate overall decision.
SELECTING AMONG VARIOUS SPILL RESPONSE OPTIONS
Approximately 3 million gallons (roughly 10,000 metric tons [tonnes]) of oil or refined petroleum product are spilled into waters of the United States every year (NRC, 2003). These spills occur anywhere from nearshore to the open sea and range from small spills of refined products such as diesel fuel to thousands of gallons of crude oil. Once a spill occurs, the slick remains at the surface until it evaporates, disperses naturally into the water column, is recovered, strands along a shoreline, or breaks up into a field of tarballs.
When containment and recovery are not possible, practical, or sufficient, the application of dispersants may help to break up the oil slick

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prior to contact with sensitive habitats and resources. In general, the use of dispersants is recommended if: (a) an oil slick threatens a sensitive coastal area and mechanical recovery is not feasible, (b) there is sufficient wave energy to break up the surface slick and mix the oil droplets into the water column, (c) the oil is of a type know to be dispersible (i.e., the type and properties of the oil favor chemical dispersion), and (d) there is sufficient potential for rapid dilution of the dispersed oil, and (e) in the course of spraying, dispersants are not applied directly to birds and mammals.
Although these general rules provide the decisionmaker with some guidance in determining when to use dispersants (i.e., when they may be effective), there is still insufficient scientific information upon which to make decisions about likely benefits and consequences of dispersant use as an oil spill countermeasure. As previously stated, the fate and effect of chemically and naturally dispersed oil has not been well documented in field trials, although there have been several published intertidal studies in tropical (Tropical Oil Pollution Investigations in Coastal Systems [TROPICS] study in Panama; Ballou et al., 1987), temperate (Searsport, Maine; Gilfillan et al., 1986) and arctic (Baffin Island Oil Spill [BIOS] Project; Blackall and Sergy, 1981) regimes. Additionally, there is disagreement about how to interpret the results of laboratory, mesocosm, and the limited field tests to date because of the difficulty of simulating or capturing an adequate range of realistic exposure conditions. There remain basic issues that need to be resolved before dispersants are more fully accepted as a response tool in a wide variety of settings. For example, the effectiveness of dispersants is sensitive to certain environmental factors (e.g., wave energy, water temperature, salinity) and certain oil properties (e.g., viscosity, degree and type of emulsification), and it cannot be accurately predicted with sufficient consistency to support decisionmaking over a wide variety of settings. Further, the acute and chronic toxicity of dispersed oil under realistic conditions has not been adequately studied to support robust decisions involving the balancing of risks among various components of the ecosystem when sensitive species or habitat may be exposed.
OPA 90 required the development of Area Contingency Plans and specifically charged Area Committees to address the use of chemical countermeasures. Most area plans now include limited pre-approvals for dispersant use in offshore waters. Chemical dispersion could be considered as a viable method in supplementing mechanical response options in nearshore waters, but a lack of sufficient information regarding dispersant effectiveness and potential effects over the wide range of settings found in nearshore areas has precluded a similar broad policy change. In an effort to address this dilemma at an appropriate scale, Regional Response Teams (RRTs) are conducting workshops to assess the risks of using chemical countermeasures in shallow coastal waters from 0 to 3 nm

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(roughly 5 km) offshore. Additional robust scientific investigations should proceed at an accelerated rate so as to support these important decision-making efforts.
In recognition of the need to prioritize dispersant research, the Minerals Management Service, National Oceanic and Atmospheric Administration, U.S. Coast Guard, and American Petroleum Institute requested that the National Research Council’s Ocean Studies Board undertake a study to explore existing and ongoing dispersant research and make recommendations for improving the knowledge base used to support dispersant decisionmaking in the United States (see Box 1-1). A similar request was put to the National Academies in the mid 1980s, leading to the publication of the 1989 NRC report Using Oil Spill Dispersants on the Sea. This current report is not truly an update of the 1989 report, as it focuses more
BOX 1-1
Statement of Task Committee on Understanding Oil Spill Dispersants: Efficacy and Effects
This study will review and evaluate existing information and ongoing research regarding the efficacy and effects of dispersants as an oil spill response technique. Focus will be placed on understanding the limitations imposed by the various methods used in these studies and to recommend steps that should be taken to better understand the efficacy of dispersant use and the effect of dispersed oil on freshwater, estuarine, and marine environments. Specifically, the committee will:
review and evaluate ongoing research and existing literature on dispersant use (including international studies) with emphasis on: a) factors controlling dispersant effectiveness (e.g., environmental conditions, dispersant application vehicles and strategies, and oil properties, particularly as the oil weathers), b) the short- and long-term fate of chemically or naturally dispersed oil, and c) the toxicological effects of chemically and naturally dispersed oil;
evaluate the adequacy of the existing information about dispersants to support risk-based decisionmaking regarding response options for a variety of spatially and temporally defined oil spills;
recommend steps that should be taken to fill existing knowledge gaps. Emphasis will be placed on how laboratory and mesoscale experiments could inform potential controlled field trials and what experimental methods are most appropriate for such tests.

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specifically on information needs to support a decision-making process that was not in existence in the late 1980s. Thus the current report revisits some topics covered in the 1989 report, while including discussions on issues that have emerged since that time. Many readers may, therefore, find the assessments and summaries in Using Oil Spill Dispersants on the Sea of value.
STUDY APPROACH AND ORGANIZATION OF THIS REPORT
Despite the significant organizational and fiscal resources committed to responding to spills in the United States each year, fairly limited funding is available to support research geared to spill response or spill response decisionmaking. While determining specific funding levels for oil spill research nationwide is beyond the scope of this study, the trend described in the key programs in Box 1-2 suggest that the overall amount of
BOX 1-2
Funding for Oil Spill Research and Development
Making decisions based on “good science” requires that an adequate scientific foundation be available. In the case of dispersant decisionmaking, this scientific foundation has developed through research and development (R&D) funded through a variety of mechanisms and supported more or less independently by various federal and state programs and industry.
Federal Support
Title VII of the Oil Pollution Act of 1990 (OPA 90) recognized the need for a comprehensive program of oil pollution research and technology development among the federal agencies, in cooperation and coordination with industry, universities, research institutions, state governments, and other nations. The legislation set up an Interagency Coordination Committee on Oil Pollution Research, (ICC; see Title VII of OPA 90, Executive Order 12777) comprised of members from the Departments of Commerce, Interior, Energy, Transportation, and Defense as well as the Environmental Protection Agency (EPA), the National Aeronautics and Space Administration, and the Federal Emergency Management Agency, to develop, implement, and coordinate such a plan. OPA 90 also authorized $19 million annually for the period from 1990 through 1995 for those R&D projects, in addition to those already underway under existing agency budgets, for this

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funding available to carry out much of the work proposed in this study is very limited and may be decreasing. Given the greater need for scientific information to support decisionmaking in nearshore waters, it will be important to coordinate research efforts to the greatest degree possible. (see Box 1-2). The committee, therefore, recognized early on that the steps recommended to address any identified knowledge gaps would need to be prioritized in some manner. After some discussion during open sessions with federal and state resource trustees, representatives of industry, and sponsors of oil spill research, the committee determined that any recommendations for future work should be related to key decision points within the overall decision-making process used in spill contingency planning and during actual spill response. This grounding in the spill response decision process (discussed in Chapter 2) helps ensure that research recommendations put forward in subsequent chapters reflect most pressing information needs.
program. (Dispersant research competes with many other worthwhile R&D programs including fundamental research into other response technologies and oil spill effects.)
Federal funding for oil spill R&D has decreased with time and, for many agencies, is non-existent (C. Manen, National Oceanic and Atmospheric Administration, Silver Spring, Maryland, written communication, 2005). For example:
U.S. Coast Guard Oil Spill research funding has remained level in the $3.5 million range. Emphasis is placed on oil spill prevention as well as oil spill response. Thus oil spill research is integrated into waterways management research, sensor systems, reduction in crew fatigue, etc., as well as oil spill clean up and response systems (K. Hansen, United States Coast Guard Research and Development Center, Groton, Connecticut, written communication, 2005).
The EPA Oil Program has provided roughly $900,000 over the last few years to the EPA Office of Research and Development (ORD) for research under the Oil Program appropriation (a separate program element in EPA’s budget). Roughly $800,000 of the total is for contract funding (D. Evans, Environmental Protection Agency, Washington, D.C., written communication, 2005).
Starting in 2004, the National Oceanic and Atmospheric Administration’s Office of Response and Restoration (OR&R) funds approximately $1.5

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million in oil spill R&D projects a year. These funds come from a mix of congressional earmarks and in-house budgets (C. Manen, National Oceanic and Atmospheric Administration, Silver Spring, Maryland, written communication, 2005).
Over the past five (5) years, the Minerals Management Service has received approximately $2.3 million dollars, annually, for oil spill response. Approximately $900,000 per year is spent on research, while approximately $1.4 million is spent on the operation and maintenance of OHMSETT (the National Oil Spill Response Test Facility located in Leonardo, New Jersey; J. Mullin, Minerals Management Service, Herndon, Virginia, written communication, 2005).
State Support
Several states (e.g., Texas, Louisiana, California, and Alaska) with particular interest in protecting natural resources from possible impacts from oil and gas development or transportation have invested funds in oil spill R&D. In several instances, these state programs rival the size of the federal programs mentioned above. For example, on March 28, 1991, the Oil Spill Prevention and Response Act (OSPRA) was adopted and signed into law by the Governor of Texas. One of the many innovative and new responsibilities mandated by OSPRA is the formation of a Research and Development component in the General Land Office (GLO) Oil Spill Prevention and Response division. Section 40.302 of OSPRA establishes the availability of $1.25 million dollars per fiscal year (R. Jamail, Texas General Land Office, Austin, written communication, 2005).
With passage of its Oil Spill Prevention and Response Act in 1993, Louisiana created the Louisiana Applied and Educational Oil Spill Research and Development Program (OSRADP). The program has an annual research budget of $500,000. Consequently, in the last 12 years the program has underwritten 91 projects from a highly diversified research agenda. (D. Davis, Louisiana State University, Baton Rouge, written communication, 2005).
Similarly, the Lempert-Keene-Seastrand Oil Spill Prevention and Response (OSPR) Act of 1991 established the oil spill response program in California and directed the Administrator of OSPR to develop a research program designed to examine the effects of oil and oil spill response technologies on the environment. Between 1993 and 1999 the program received $600,000 a year from OSPR and additional $50,000 to $200,000 a year from government and oil industry funding sources. The research program was temporarily discontinued between 2000 and 2002 and reinitiated in 2003 with an annual budget of approximately $300,000 (M. Sowby, California Department of Fish and Game Office of Spill Prevention and Response, Sacramento, written communication, 2005).
Alaska does not have a formally established oil spill research program;

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however, it has invested considerable time and resources in updating the baseline knowledge regarding the use of dispersants. As a result of a legal judgment from the T/V Exxon Valdez oil spill, funds were appropriated for use by the state to enhance oil spill research and development. A total of $2,500,000 was made available to the Alaska Department of Environmental Conservation for projects under this program. Research projects carried out to date have focused on understanding the effectiveness of dispersants, fate and effect, and uncertainties associated with exposure tolerances of marine species to potentially acute, sublethal, and chronic toxicity levels from the dispersant and dispersed oil (L. Pearson, Alaska Department of Environmental Conservation, Juneau, written communication, 2005).
Industry Support (J. Clark, ExxonMobil Research and Engineering Company, Fairfax, Virginia, written communication, 2005; and R. Rorick, American Petroleum Institute, Washington, D.C., written communication, 2005)
Historically, the petroleum industry has supported research on dispersants as part of American Petroleum Institute (API) funded programs, R&D programs funded through spill response organizations such as the Marine Spill Response Corporation (MSRC), and through joint industry or joint industry/government projects funded to address specific issues. During 1970–1995, a broad diversity of oil spill R&D was organized and sponsored through API (Gould and Lindstedt-Siva, 1991; Aurand et al., 2001) with a budget of approximately $50 million, about one-third of which focused on dispersants. At the same time, individual petroleum companies, API, and MSRC also contributed funding for additional studies as part of large-scale, million dollar government/industry projects conducted in Europe. In addition, individual companies organized and/or conducted fundamental and applied research on dispersant use in oil spill response at a cost of several million dollars a year.
In subsequent years, API continued funding many of these dispersant projects, supporting them to completion over the next 5 years in the range of $200 to $400K per year. These studies included a variety of field, laboratory, and mesocosm tests (including supporting the construction of the test system now known as the Shoreline Environmental Research Facility at Texas A&M University, Corpus Christi) and targeted surveys and communication guides for spill responders and decisionmakers (Aurand et al., 2001).
In recent years, organized research programs at MSRC have ended and API support for research has been greatly reduced. As companies continue to evolve into organizations that manage and prioritize their technical information needs based on a global perspective, the focus of research projects has been on development and testing of basic principles and concepts that have broad applicability. It has become increasingly difficult to develop support for large research projects that may be driven by local or regional issues.

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Chapters 3, 4, and 5 discuss lessons learned from an extensive review of the existing literature dealing with the effectiveness of dispersants, as well as the fate and effects of dispersed oil, with a major focus on studies completed since the release of the 1989 NRC report Using Oil Spill Dispersants on the Sea. Chapter 3 provides a detailed discussion of relevant petroleum properties and geochemical processes and the mode of action of various dispersants. In addition, it includes an in-depth discussion of the current understanding of dispersant effectiveness and provides specific recommendations for developing an adequate understanding of effectiveness to support more informed decisions regarding dispersant use in nearshore settings. Chapter 4 explores physio-chemical and biological processes that control the dispersion and fate of oil droplets and thus constrain the concentrations of various petroleum compounds in the water column. In addition, the role of modeling and monitoring to better support decisionmaking is explored, and specific recommendations to improve information needed to support decisionmaking are provided. Chapter 5 provides an in-depth analysis of toxicological studies that focus on dispersants or dispersed oil. By summarizing the salient points from existing reports and recommending specific additional, needed toxicological work, Chapter 5 provides guidance on efforts to better understand the effects of dispersed oil—a key component of effective decisions involving difficult trade-offs among sensitive species or habitats. Chapter 6 summarizes the key findings and recommendations of the previous chapters and organizes them into what is intended to be a coherent research plan to inform and coordinate to the degree possible research carried out or sponsored by federal and state entities, industry, and academia.